Long-term evolution (LTE) is a wireless standard which serves a large number of user equipments (UEs). The LTE standard uses a minimum bandwidth of 180 KHz for communication with the devices. In downlink (DL), the LTE uses orthogonal frequency division multiple access (OFDMA) and single-carrier FDMA (SC-FDMA) in an uplink (UL). With 15 KHz subcarrier spacing, there are 12 subcarriers available for scheduling pilot tones. The LTE defines three physical layer channels in the UL namely physical uplink shared channel (PUSCH), which carries user data and some control information, physical uplink control channel (PUCCH) which carries uplink feedback data and physical random access channel (PRACH) for initial access purposes.
In order to improve reliability and efficiency of the control channel, the LTE defines a retransmission mechanism which involves in acknowledgement (ACK) and non-acknowledgement (NACK) transmissions. Feedback signals are sent by UEs in response to successful reception of a downlink data packet are termed as ACKs and messages that indicate failure of reception of certain block of data are termed as NACKs. In uplink, UEs are scheduled such that:                (1) The UEs does not have uplink data to transmit but they do have uplink feedback data such as ACK/NACK, channel quality feedback and so on. In such cases, the UEs transmit feedback data in the PUCCH.        (2) The UEs have both feedback data and uplink data to transmit. The feedback data is multiplexed with uplink data and transmitted on the PUSCH.        
Depending on type of feedback data being transmitted, the PUCCH is categorized into various formats. Format 1 is used for carrying a positive scheduling request, Format 1A to transmit 1 bit ACK/NACK in case of single code word downlink transmission and format 1B to transmit 2 bit ACK/NACK in case of two code word downlink transmission. Format 2 for sending stand-alone CSI report, Format 2A carries CSI report multiplexed with 1 bit ACK/NACK and Format 2B carries CSI report multiplexed with 2 bit ACK/NACK.
The PUCCH is structured to exploit frequency diversity to minimize the resources needed for feedback data transmission. Accordingly, frequency resource for PUCCH is configured at edges of uplink system bandwidth. Each PUCCH transmission occupies one resource block (RB) at or near the edge of system bandwidth followed with 2nd resource block placed at or near opposite edge of system bandwidth. Each resource block constitutes of 12 OFDM sub-carriers and 6 or 7 OFDM symbols depending on nature of cyclic prefix being used.
In the existing systems, channel state for each UE is estimated based on pilot codes transmitted on each tone (sub-carrier) and symbol, individually for each UE. Thus, in the existing systems, the channel state of each UE estimated individually which consumes more number of cycle counts (i.e., processing time) required for detecting control data at a receiver.